To travel from Japan to China, there is a direct ferry connection from Osaka (Japan) to Shanghai (China). Both cities are connected to the national railway network.
Another option is to travel first from Japan to Busan (South-Korea) by ferry, cross South Korea by train to Incheon. And take another ferry from Incheon (South Korea) to Qingdao (China), from where you continue by train to your destination in China.
If you want to travel from Japan to South Korea, you have to include a ferry. Daily ferry connections are available from Shimonoseki (Japan) to Busan (South Korea) and from Sakaiminato (Japan) to Donghae (South Korea). All cities are connected to the national railway networks and easy to reach.
To travel from Japan to Russia, you have to include a ferry for example on the route from Sakaiminato (Japan) to Vladivostok (Russia). Ferry connection once per week with two nights on board. Both cities, Sakaiminato (Japan) and Vladivostok (Russia), are connected to the national rail network.